Effects of landscape disturbance on animal communities in Lake Tanganyika, East Africa

Watershed deforestation, road building, and other anthropogenic activities result in sediment inundation of lacustrine habitats. In Lake Tanganyika, this threatens the survival of many rock-dwelling species by altering the structure and quality of rocky habitats. We investigated the relationship between habitat quality, as related to watershed disturbance intensity, and the biodiversity of faunal communities at three rocky littoral sites of low, moderate, and high disturbance. Turbidity measurements and other environmental observations confirmed that our lake sites represented a gradient of disturbance conditions. We documented differences in species density (number of species per constant area or time), species richness, abundance, and trophic ecology for fishes, molluscs, and ostracods. Fish censuses were performed by scuba divers at 1-20 m and by remotely operated vehicle (ROV) at 40-80 m. In the fish surveys, abundance, species density and richness, and herbivory reached their maxima at intermediate water depths. The depth range of herbivores, however, was restricted at higher-disturbance sites. The ROV fish surveys at the high-disturbance site showed high species richness despite low species density and abundance, and piscivores were proportionally more prevalent than in all other surveys. Molluscs censused by diver quadrats and sieve samples showed decreasing species richness and species density (sieve samples only) with increasing disturbance and no significant abundance trend. Ostracod species richness was similar between low- and moderate-disturbance sites but was markedly lower at the high-disturbance site (species density and abundance data were not available). Our faunal analyses suggest that all three taxonomic groups are negatively affected by sediment inundation but may have varying response thresholds to disturbance. Further, this study emphasized the utility of using complementary survey techniques to monitor and ultimately manage biodiversity in complex freshwater ecosystems.